The present invention relates to an apparatus for measuring linear distances, and more particularly to a measuring tape having a spring-powered return mechanism.
Measuring tapes having spring-powered return mechanisms are well-known in the art. In such devices the tape is wound around the outside of a rotatable drum or reel mounted within a casing. A coil spring made of flat strip steel or other suitable material is disposed inside the drum. The coil spring becomes stress-wound as the tape is withdrawn from the casing and imparts its stored energy to rotate the drum when it is desired to retract the tape into the casing. The measuring tapes shown in U.S. Pat. Nos. 3,578,259; 3,521,831; 3,519,220; 3,519,219; 3,499,612 and 3,415,461, are exemplary of such prior art devices.
For relatively short tapes of 25 feet or less, the above-described prior art devices are effective and easily used. However, for tapes of greater length, particularly those in excess of 50 or 100 feet, the concentric arrangement of tape and coil spring necessitates a relatively large and bulky device that is difficult to handle and use. Consequently, measuring tapes of such length are usually not provided with spring-powered return mechanisms, but rather utilize a simple hand crank for rewinding the tape. Inasmuch as space for the coil spring is not required in such devices, the rotatable drum or reel upon which the tape is wound may be relatively small in diameter, thus minimizing the size of the device. However, because the diameter of the drum is, by design, relatively small, each turn of the crank retracts only a short length of tape, particularly in the initial stages of the rewinding operation. Thus, rewinding such long tapes by hand is a slow and tedious procedure.